1. Field of the Invention
The present invention generally relates to integrated circuit designs and more particularly to an improved method of comparing designs with simulated images of the designs.
2. Description of the Related Art
The design of integrated circuits involves multiple stages of distinctly different types of activity. More specifically, a designer creates a schematic circuit to achieve specific goals. The schematic circuit is an arrangement of various logic devices that are connected to perform some logical activity. The designer then generally uses a computer-aided design (CAD) program to prepare a design data set. The design data set is a theoretical illustration of conducting, insulating and semiconducting shapes which should be manufactured to form the logic devices shown in the schematic circuit. The design data does not include or account for process variations or manufacturing mask and wafer effects which would occur during actual production of the items shown in the design data set.
In order to promote the production of working logic devices that achieve the designer""s goals including yield, cost and performance, the design data set is processed through various algorithms which account for processing variations and manufacturing effects, such as simulation tools that may include Optical Proximity Correction (OPC) capabilities. Such programs produce simulation data based on the design data set.
The simulation data is then checked to determine whether the design data set should be modified to eliminate any possible manufacturing defects, such as incompletely formed structures, improperly formed intersections, unwanted intersections (e.g., short circuits) or other similar defects. Once the simulation data indicates that the design data set would produce acceptable working items, the design data set is transferred to a manufacturing format to produce lithographic masks and other similar items necessary to produce the integrated circuit.
One drawback of this system is the fact that the simulation is run on a different tool (program) than the one used to create the design. Another drawback is the inability to check such things as the effect of OPC on overlay tolerance on the simulation tool.
Further, the iterative process of repeatedly modifying the design data set and checking the simulation data is laborious, time-consuming and substantially increases the cost of the items produced. Therefore, there is a need to reduce the expensive and laborious process of separately designing and simulating logic circuit designs.
It is, therefore, an object of the present invention to provide a structure and method for creating a photomask data set that includes inputting a design data set which has at least two levels, creating a simulated printed data set which has the same levels by applying a lithographic or other simulation model to each level of the design data set under consideration, merging each level of the design data set with each corresponding level of the simulated printed data set to produce a merged design data set, applying at least one test to either the merged design data set or the simulated printed data set, and correcting the design data set based on results of the test to produce a corrected design data set. The creation of the simulated printed data, merging, applying the test and correcting processes are repeated using the corrected design data set until the corrected design data set passes the test or no further corrections can be made. The corrected design data set is output as the photomask data set.
The converted format of the simulated printed data set complies with the format of the design data set. The merging includes overlaying each level of the design data set on each corresponding level of the simulated printed data to produce overlaid images. The test includes identifying differences between the design data and the simulated printed data. The creation of the simulated printed data set and the merging are performed sequentially in near real time as the design data set is corrected. The creation of the simulated printed data modifies the design data set to include predicted manufacturing changes.
A second embodiment of the invention includes inputting design data for at least two levels, producing simulated printed data from the design data, overlaying the simulated printed data levels to produce overlaid data, testing the overlaid data, correcting the design data based on results of the test to produce corrected design data, repeating the process using the corrected design data until the corrected design data passes the testing, and outputting the corrected design data as the photomask data.
The format of the simulated printed data is converted to comply with the format of the design data. The testing comprises checking relationships such as spaces or overlap areas between shapes on different levels. The producing of the simulated printed data and the overlaying can be performed in real time as the design data is corrected. The producing of the simulated printed data modifies the design data to include predicted manufacturing changes. The design and simulated printed data include multiple levels. The overlaid data includes multiple levels of overlaid images which are distinguished by color, shading or brightness.
Another embodiment of the invention includes inputting design data, producing simulated printed data from the design data, altering the format of the simulated printed data to comply with the format of the design data, overlaying the design data to detect differences between the design data and the simulated printed data, correcting the design data based on the differences between the design data and the simulated printed data to produce corrected design data, repeating the process using the corrected design data until the corrected design data is functionally the same as the design data, and outputting the corrected design data as the photomask data.
The producing of the simulated printed data, which modifies the design data to include predicted manufacturing changes, and the overlaying are performed in real time as the design data is corrected. The design and simulated printed data include multiple levels, and the overlaying produces multiple levels of overlaid images which can be distinguished by color, shading or brightness.
The ability to view simulated wafer printed images interactively on a screen with the original design helps the designer determine what needs to be fixed or adjusted on the original design. The invention also determines if the overlap area between two levels is large enough for contact between the two levels, given that there are variations in overlay between the two levels.
The ability to view the overlap is important but the ability to determine if variations of overlap can be tolerated can be extremely important. A contour plot (plot of constant intensity of aerial images, wafer outline of shapes in a developed or undeveloped resist) can be easily placed over the original design data but the ability of the CAD tool to determine what shapes are closed and therefore moveable is not obvious by just looking at the contour data itself.
Thus, the invention includes an algorithm to determine what shapes are closed and therefore moveable prior to loading the data into the CAD programs. The CAD programs move the shapes, calculate the area of shapes, calculate intersection area between two levels, expand or shrink the shapes, etc.
The invention allows device designers to simultaneously view both as designed images and simulated printed images on a standard design system and to manipulate both image types with the standard tool kits of the design system. The invention overcomes the problems of conventional systems by converting the simulation data to a format which is consistent with the format of the design data. By overlaying the simulation data on the design data, the specific corrections which should be made to the design data set become easier to recognize. Further, the invention may produce the simulation data as the designer creates/modifies the design data set so that the conventional iterative process of repeatedly producing the simulation data, viewing the results in a second tool, modifying the design data set and viewing those results in the CAD tool is simplified.